Current process schemes for producing alkylamines from alcohols or their corresponding ethers require separation and recycling of certain of the amine products to obtain the desired alkylamines product distribution. For example, when using an amorphous silica-alumina catalyst for the production of the mono-, di- and trisubstituted methylamines from methanol and ammonia, such recycling is necessary because the product distribution of the methylamines is controlled by the rapid equilibria of the amines among themselves and ammonia.
The following reaction equations (1-3) show the production of the mono-, di- and trialkylamines from the starting materials comprising the alkanol (ROH) and ammonia: EQU ROH+NH.sub.3 .fwdarw.RNH.sub.2 +H.sub.2 O (1) EQU ROH+RNH.sub.2 .fwdarw.R.sub.2 NH+H.sub.2 O (2) EQU ROH+R.sub.2 NH.fwdarw.R.sub.3 N+H.sub.2 O (3)
In addition to the above pathways for the three alkylamine products, the following equilibrium reaction equations (4-6) show another mechanism responsible for the alkylamines product distribution: EQU R.sub.2 NH+NH.sub.3 .revreaction.2RNH.sub.2 ( 4) EQU R.sub.3 N+NH.sub.3 .revreaction.R.sub.2 NH+RNH.sub.2 ( 5) EQU R.sub.3 N+RNH.sub.2 .revreaction.2R.sub.2 NH (6)
At each set of conversion conditions comprising temperature, pressure, catalyst, ammonia:alcohol feed ratio and flow rate, the above reaction equations 1-6, particularly equilibrium reaction equations 4-6, necessarily yield an equilibrium controlled distribution of the mono-, di- and trialkylamines.
For example, with respect to the production of the methylamines from methanol and ammonia under given conversion conditions, these equilibria limit the amount of each methylamine in the product stream. Therefore, if the desired amine product is dimethylamine, the mono- and trisubstituted products typically are separated from the product stream and recycled to the reaction zone along with the excess ammonia to produce more dimethylamine from these less desired amines via the equilibrium reactions 4-6. However, the product stream will still comprise an equilibrium controlled methylamines product ratio. Such recycling of some of the amines product is required in amines processes whenever the composition of the desired product stream is other than the equilibria controlled distribution of the three amines.
One means for controlling the product distribution in a catalytic reaction between an alcohol and ammonia to produce alkylamines is disclosed in U.S. Pat. No. 3,384,667. This patent teaches a methed for producing monosubstituted and disubstituted amines in preference to trisubstituted amines by reacting ammonia with an alcohol in the presence of particular crystalline metal aluminosilicate catalysts. Such aluminosilicate catalysts have become known as shape selective catalysts.
U.S. Pat. No. 4,229,374 discloses a process for producing tertiary amines by reacting alcohols with ammonia, primary amines or secondary amines in the presence of a catalyst which comprises a mixture of copper, tin and an alkali metal supported on a suitable carrier.
U.S. Pat. No. 4,254,061 discloses a process for producing monomethylamine by reacting methanol and ammonia in such amounts so as to provide a C:N ratio, from the methanol and ammonia reactants, of 0.5-1.5 over a particular zeolite catalyst.
These prior art processes do not permit the production of a mono-, di- and trisubstituted alkylamine product stream in nonequilibrium controlled distribution. Furthermore, recycling of at least a portion of a less or undesired alkylamine is usually required in order to maximize the production of the desired alkylamines.
The amination reactions are exothermic. Thus, in an adiabatic plugged flow reactor for the production of methylamines, for example, the temperature rises by 150.degree.-400.degree. F. (66.degree.-232.degree. C.) depending on the ammonia:methanol feed ratio. The maximum allowable reactor temperature for methylamines is 800.degree. F. (427.degree. C.), above which thermal reactions yielding coke and cracked by-products make the process inoperative.
The present silica-alumina catalysts require feed temperatures above 600.degree. F. (316.degree. C.) to obtain commercial methylamines production requirements. With a starting temperature of 600.degree. F. (316.degree. C.), the molar feed ratio of ammonia-methanol must be higher than 2 for the maximum temperature in an adiabatic reactor to be less than 800.degree. F. (427.degree. C.). Therefore, greater than two-fold excess ammonia over the stoichiometric requirement must be used to avoid coking and cracking. Use of such excess ammonia means large ammonia separation stills to recycle the ammonia.